X-ray tube



Oct. 11, 1927. 1,645,304

J.- SLEPIAN X-RAY TUBE Filed April 1, 1922 2 Sheets-Sheet 2 INVENTORJoseph Slap/m.

7 ATTORNEY Patented a. 11, 1927.

UNITED STATES PATENT OFFICE JOSEPH SLEPIAN, OF SWISSVALE, PENNSYLVANIA,4mm "1'0 WESTINGHOUSE ELECTBQIG a MANUFACTURING COMPANY, A CORPORATION01' PENNSYLVANIA.

x-BAY TUBE.

Application filed April 1,

My invention relates to electron-tube devices and articularly to suchdevices as A are adapted to generate X-rays.

An object of my inventlon is to prov de I an electron tube having anelectron-emitting element and a co-operating element or target, whereinthe electrons, em1tted from said source are caused to attain a velocitgreater .than that which is given by the in uence of any electrostatic,potentials impressed upon said elements.

Another object of my invention 1s to provide an X'-ray tube which iscapable of producing useful X-rays with relatlvely low 18 voltages,-incomparison to the voltages heretofore considered necessary.

A further object of my invention is to provide an X-ray tube which isslmple 1n design and in construction and which has 20 highly desirableoperating characteristics.

Heretofore, in order to produce X-rays having suflicient penetration orhardness to be useful, it has beennece'ssary to employ relatively highvoltages, as from 20,000

28 volts to 100,000 volts, or more. Such X-ray tubes comprise anelectron-emitting cathode and a target upon which electrons emitted fromthe cathode are caused to impinge with extremely high velocity. Themaxi- 3o mum velocity with which the electrons strike the target hasheretofore been determined solely by the difierence in potential betweenthe cathode and the target. Tubes employing potential differences of100,000v0lts or more are now in common use, and the tendency of the artis toward a constantly increasing voltage.

It is obvious that the use of such voltages constitutes a great elementof risk, especially when it is necessary to work in confined quarters orto bring the tube close to the body of a patient under treatment.

According to my invention, I cause the electrons which produce theX-rays to attain an extremely high velocity without depending upon theusual direct electrostatic action between the cathode and the target,which, as stated, requires the use of extremely high potentials.

The desired result is obtained by subjecting the electrons to theinductive effects of a varying magnetic field. It is well known that avarying magnetic field has associated therewith an electric field, the

.mode of operation, the circuit arr 1922. Serial No. 545,030.

field, and it is this electric field which I utilize to impart velocityto the electrons, all as will be explained more fully hereinafter.

With these and other objects in view, my invention further consists inthe nature, the ment and the constructional details hereinafter morefully-set forth andclaimed.

In the drawing, Fighre 1 is .a diagrammatic re resentation'of circuitsand apparatus em .ody' g my invention, shown partially in section;

Flg. 2 is a top plan view of the evacuated container of Fig. 1,illustrating the path taken' by the electrons when under the infiuenceof an electrostaticforce between the cathode and the target and whenunder the influence of an additional transverse magnetic field;

Fig. 3 is a view similar tothat of Fig. 2, showing the efi'ect upon theelectron path of a varying magnetic field;

Fig. 4 is a horizontal sectional view of a structure embodying thepreferred formof my device, the section-plane being indicated by theline IV-IV in Fig. 5;

Fig. 5 is a longitudinal section on the hne V-V of Fig. 4. I

In Fig. 1 is shown a. disk-sha e electron tube 1 having oppositeparallel aces 2 and 2 An electron-emitting element 4, which 1s energlzedfrom a source 5 of direct-current energy, is centrally disposed withinthe tube 1. An anode or target 6 is disposed adjacent the outerperiphery of the tube 1.

A conductor 7 serves to connect the ano de 6 and 'the cathode 4 and mayinclude a direct-current source of energy 8, the effect Of"Wl1lCh 1s todraw the electrons from the .surface of the cathode 4, and thereby givethe initial electron loop aslarge a radius as possible; The advantage ofthis condit1on willr'be explained hereinafter.

A magnetic field, which is t-ransverse to the plane of the tube 1, isobtained by dis-- posingthe disk-shaped pole pieces 9 and 11 of asubstantiall U-shape magnet 12 adja'ce'nt opposite aces of the tube 1.The magnet 12 may be excited by means of a magnetizing winding 13, whichis wound around a curved ortion 14 of the magnet 12 and energized om asource 15 of directcurrent energy. An input or exciting C011 16 isdisposed in the plane of the tube 1 immediately adjacent-the peripherythereof and may be excited from a source 17 o alternating current orcondenser discharge.

When neither of the magnetizing windin s 13 and 16 is excited and apotential di erence is established between the electron-emitting element4- and the anode 6, the electrons emitted from the element 4 are causedto follow the electrostatic lines of force existing between the twoelements just mentioned as indicated by dotted lmes a in Fig. 2. I-lere,it will be noted that the velocity of the electrons im inging upon thetarget 6 is determined sole y by the potential difference existinbetween the cathode 4 and the target 6. s hereinbefore stated, it hasbeen found necessary to resort to potentials of the order of 100,000volts or more to produce X-rays having useful penetration values.

When the direct-current exciting windin 13 is energized by the enersource 15, a unidirectional magnetic fiel is roduced, which istransverse to the plane 0 the electron path, and it is found that thecurrent to the anode ceases and that the electrons are caused to moveabout the cathode 4 in substantially closed paths or loops, as indicatedby curved lines 6 of Fig. 2. This has been proved mathematically and isan effect which is well known in the art.

When the alternating-current exciting winding 16 is energized and avarying electric field is produced which lies substantially in the planeof the. container 1, the kinetic energy or velocity of the electrons isgreatly increased foreach complete traversal of its path 6. The actionis not unlike that observed in the ordinary transformer, the excitingwinding 16 corresponding to the primary winding of the transformer andthe path represented by one complete revolution of an electron as asecondary coil. In the transformer, the potential of the secondarywinding increases with the number of turns and the time rate of changeof the flux threading the same. Similarly, in my device, the potentialenergy dr velocity of an electron increases with each complete traversalof its path and also with increases in the diameter of its path.

At first hand, it would appear that an electron would continue torevolve in its orbit indefinitely and that the velocity thereof wouldtend to become infinite in value. However, it may be demonstratedmathematically that the action of the centrifugal forces operating uponthe electron are such that it tends to traverse a spiral path of everincreasing radius until it impinges upon the target, as illustrated bythe spiral curve c of Fig. 3, The exact nature of the spiral produced bythe winding 13 an path will be de endent upon the initial veocity of theeectrons, which are emitted from the cathode4, as well as upon therelative valuesof t e constant ma etic field the alternating magneticfield produced by the windin 16.

en the electrons finally impinge upon the target 6, their kinetic energyhas attained such value that X-rays are produced of a penetrating valueequivalent to that of X-rays which could be produced heretofore only bythe application of very much higher external potentials between thecathode 4 and the anode 6 when utilizing the influence of the directelectrostatic action alone. 7 V The device of Fig. 1, however, has aserious limitation by reason of the fact that the maximum practicallyattainable initial radius of the electron loop 6 is relatively smalland, hence, alternating currents of extremely large values and of highfrequencies must be applied to the exciting coil 16 to produce thedesired results hereinbefore stated- In the referred form, as shown inFigs. 4 and v5, t e cathode 4 and the target 6 are so disposed that thepath of the electrons,

upon the electrons comin under the influence of the electrostatic eld,which is associated with the varying magnetic field, has an initial pathof such' radius as to obviate the difliculties hereinbefore mentioned.

The structure there shown comprises a highly evacuated toroidal tube 17having the electron-emitting element 4 dis osed immediately adjacent theinner perip ery thereof and the target 6 disposed diametricallyopposite, and adjacent to, the outer peripherythereof. "A lamiriatediron core member 18, similar to that employed in "transformers of thewell known shell type, is built around the envelope 17 in such mannerthat the same is linked by two -magnetic circuits 19 and 21 having aportion 22 in common, as indicated by the arrows of Fig. 5. The commonportion 22 of the two magnetic circuits 19 and 21 is encircled by amagnetizing winding 23 which may be associated with a source 24 ofalternating current or condenser discharge by conductors 25 and 26.

Mounted above and below the container 17 are a series ofsegmentally-shaped guiding magnets 27 and 28. The several magnets are sodisposed upon the opposing faces of the tube 17 as to produce transversefields near the inner and outer walls of the tube in order to produce astrong crowding action upon the electrons within the same; that is tosay, an eflect which tends to deflect the electrons from the inner andouter walls and to maintain them in a circular path which is midwaybetween the inner and the outer 3X 10*D. To obtain 7 joining the cathode4 and the target 6 may or may not include an energy source 8.

hen the filamentA is energized, electrons are driven off, some of thesame moving toward the left in Fig. 4. The electrons are deflected fromthe inner and outer peripheries of the container by the action of thestrong magnetic fields which exist there by reason of the resence ofthe-magnets 27 and 28. Hence, e ectrons are caused to revolve around thecontrol magnetizable core in a substantially circular path. The effectof the varying flux in the control core, during one half-cycle of thealternating current, is to develop an accelerating potential, bytransformer action, causing the electrons to increase in velocity, forreasons hereinbefore mentioned. Asthe electrons increase in velocity,the effect of the increasing centrifugal forces causes them to penetratefarther and farther into the magnetic field adjacent to the outerperiphery and, ultimately, to strike the anode 6 and produce X-rays.

For illustrative purposes, I will give a practical example of thesolution of certain design problems connected with my invention,although it is to be understood that my invention is not necessarilylimited to any particular desi Assuming that the highest vacuum t at canbe maintained is 10 mm. of mercury, the mean free path of an electron,which it will travel before striking a molecule, will be approximately500,000 cm. If an electron velocity corresponding to 100,000 voltpotential is desired,

a voltage-gradient of? volts per cm. is necessary for optimum operatingconditions. If D is the diameter of the circular path traversed by anelectron, and 2B is the cross-sectional area of themagnetizable 'coreextending therethrough, the maximum total flux is and, since the lengthof a turn is 1rD, the

volts per cm. are

% 10- fDB.

Assuming a flux density of B=10,000 and a frequency of f=60, the voltsper cm. are

D= cm., approximately. If a freqency of f=600 cycles. per second wereemployed, the

volts per cm.,

diameter of the meanpath of the electrons would be.D=7 cm.,approximately.

While I have shown my inventlon embodied in'two difl'erentconstructions, it is apparent that it is not to be limited thereby,-.and that the broad, principle, WhlCh has prior art or indicated by theappended claims.

I claim as my-invention:

1. The method of increasing the energy of an electron which consists insubjecting said electron to the influence of a varying magnetic field ofsuflicient magnitude to cause said electron to move in a path comprisingrepetitions approximately like whorls the energy of said electronincreasing with each traverse of a repetition.

2. The method of increasing the energy of an electron which consists insubjecting said electron to the influence of an electric field and avarying magnetic field, the rate of change of said magnetic field beingsuificient to cause said electron to move in a path comprisingrepetitions approximately like whorls, the plane of said ath coincidingwith that of said electric eld, whereby the velocity of said electronwill increase with each traverse of one of said repetitions in saidpath.

3. The method of increasing the velocity of an electron which consistsin subjecting it to the influence of an electric field and of a varyingmagnetic field of sufiicient magnitude and rate of change to cause theelectron to traverse a spiral path, the direction of said magnetic fieldbeing such that the planeof said ath will coincide with that of saidelectric eld, whereby the velocity of said electron will increase withincreased length of said spiral and will correspond to a potentialexceeding that producing said electric field.

4. An electron tube having a source of electrons and an electrode, saidsource and said electrode constituting the limits of the electron pathand means for establishing a varying magnetic field across said path ofan average intensity sufficient to prevent the electrons traveling thewhole length of said path in a single whorl and of a rate of variationsufficient to increase by a substanelectrons to move in nearly closedpaths and means for causing the velocities of said elec trons toincrease throughout the lengths of said paths.

'tial amount the magnitude of the impact 6. An electron tube incombination with means for causing the electrons'to move 1n a fiatspiral path of more than one whorl.

7. An electron tube com rising a source of electrons, means for estalishin ing magnetic field in the vicinity t ereof of sufiicientintensity and suflicient rate of variation to cause said electrons totraverse paths of'increasingly larger diameters embracing a portion ofsaid varylng magnetlc 8. An electron-tube device comprising an evacuatedtoroidal envelope, a source of electron emission disposed adjacent theinner periphery of said envelope, an anode disposed adjacent the outerperi hery of said envelope and means for estab ishing a varying magneticfield so disposed as to link said envelope.

9. 'An electron-tube device comprising an annular-shape envelope, anelectron-emitting element disposed adjacent to the inner peripherythereof, a second element disposed adjacent to the outer peripherythereof, means for etablishing forces in said tube tending to constrainelectrons to a closed path extending around the annulas within theenvelope and means for developing an accelerating force acting upon saidelectrons moving in said path. v

10. An X-ray tube having an electronemitting element and a co-operatingele ment, means for producing a field of force between said elements andmeans acting throughout substantially the Whole travel of the electronsfor increasing the kinetic energy of the electrons emitted from saidelectron-emitting element to values higher than that produced by saidfield, of force.

11. An electron tube comprising an annular shaped envelope having anelectronemitting element and a co -Operating element suitably disposedtherein and means for establishing a varying magnetic field so disposedas to link said envelope.

12. An electron tube comprising an annular-shape envelope having anelectron-emitting element and a co-operating anode suitably disposedtherein, means establishing forces in said tube tending to driveelectrons circumferentially around said tubes and means for establishingstrong magnetic fields adjacent the inner and outer circumferences ofsaid envelope tending to maintain the orbits of said electronssubstantially circular.

13. An electron tube comprising an annular-shape envelope havingopposite faces, an electron-emitting element and a co-operating elementsuitably disposed therein, means establishing forces in said tubetending to drive electrons emitted from said elementcircumferentiallyaround said tube and guiding ma ets so disposed uponthe opposite faces 0 said envelope as to establish strong a varyma neticfields adjacent the inner and outer peripheries of said envelope tendingto maintain the orbits of said electrons substantially circular.

14. An electron-tube toroidal envelope, an electron-emittin element anda co-op'erating element suitably disposed therein, a maghetizable memberadapted to form a magnetic circuit linkin sai envelope, means forenergizing sai memberand means for establishing magnetlc fieldstransverseto the plane of said envelope adjacent the inner and the outerperipheries thereof, said fields bein such that electrons are repulsedwhen ten ing to enter the same.

15, An electron-tube device comprising a toroidal envelope, anelectron-emitting element disposed adjacent the inner periphery thereof,a co-operating; element disposed adjacent to the outer peripherythereof, a magnetizable member adapted to form a magnetic circuitlinking .said envelope, means for variablyenergizing said member, andguiding magnets so d1sposed-as to establish a magnetic field transverseto the plane of said envelope adjacent to the inner and the outerperipheries thereof, said fields being such that repulsive forces areexerted upon electrons tending to enter the same.

16. An electron-tube device comprising an evacuated envelope, :1 sourceof electrons therein spaced from the outer periphery thereof, means fordeveloping forces tending to cause said electrons to traverse closedpaths, comprising repetitions approximately like whorls, the energy ofsaid electron increasing with each traverse of a repetition, an anodewithin said envelope substantiall outside of said paths, and means forpro ucing a varying flux linking said paths and varying in suchdirection as to impress an acceleratingpotential upon said electrons,whereby said paths ultimately increase in diameter sufliciently for theelectrons to impinge upon said anode.

17. An electron-tube device comprising an evacuated envelope, 2. sourceof electrons therein spaced from the outer periphery thereof, means fordeveloping forces tending to causes said electrons to traverse aninitial substantially circular path of predetermined diameter, an' anodewithin said envelope substantially outside of said path, and means forproducing a varying flux linkin said path and varying continuously insuc direction as to impress accelerating potentials upon said electrons,whereby said path ultimately increases in diameter sufiiciently for theelectrons to impinge'upon said anode, the continuous unidirectionalvariation in flux being continued at least for a period commensuratewith the mean time required foran electron to travel from cathode tonode a device comprising a 18. An electron-tube device comprising asubstantially toroidal evacuated envelope, a source of electrons thereinspaced from the outer wall thereof, magnetic means operative near thewalls thereof for developing forces normally tending to restrict themovement of the electrons to paths near the center of thecross-sectional area of the evacuated space, an anode within saidenveloge adjacentthe outer wall thereof and outsi e of the normalelectron-paths, and means for producing a varying flux linking saidpaths and varying in such direction as to impress an acceleratingpotential upon said electrons, whereby said paths ultimately increase indiameter sufficiently for the electrons to impinge upon said anode.

19. An electron-tube device comprising a substantially toroidalevacuated envelope, a source of electrons therein spaced from the outerwall thereof, magnetic means operative' near the walls thereof fordeveloping forces normally tending to restrict the movement of theelectrons to paths near the center of the cross-sectional area of theevacuated space, an anode within said envelope adjacent the outer wallthereof and outside of the normal electron-paths, and means forproducing an alternating magnetic flux linking said toroidal container,whereby, during at least one half-cycle of said alternating flux, saidelectron-paths ultimately increase in diameter sufliciently for theelectrons to impinge upon said anode, the half-period for saidalternating flux being at least-large enough to be commensurate with themean time required for an electron to travel from catode to anode.

In testimony whereof, I have hereunto subscribed my name this 29th dayof March,

JOSEPH SLEPIAN.

